Image-assisted method for estimating local stiffness of soft tissues and calibration of bias due to aqueous humor effect

The stiffness of a material is related to the material's elastic modulus. Based on the measured stiffness of soft tissues during palpation, medical doctors can distinguish pathological tissues. In this study, an image-assisted method is developed for estimating the elastic modulus of soft tissues in order to quantify the local stiffness for the palpation purpose. The method uses a modified contact model which relates the contact radius and contact force to estimate the elastic modulus of objects. The modified contact model was derived from the Hertz contact model and calibrated by the finite element method. Experimental results on polydimethylsiloxane show that the method can accurately predict the elastic modulus. In this study the porcine liver was employed as an example of the soft tissues. When a porcine liver is tested, aqueous humors appear on the surface of the tissue, creating a false contact area. An additional method for correcting the contact area error is also proposed. After the correction, the elastic modulus of six porcine liver samples was found to be 40.4 ± 24.1 kPa. The results reveal that the image-assisted method is feasible for the porcine liver. It may also be applied to other soft tissues.